1. Field of Invention
This invention relates to an interference spectrometer, and more particularly to such spectrometer having improved vibration resistance and improved power consumption.
2. Description of the Prior Art
An interference spectrometer causes interference by dividing an output light from a light source into two optical paths and by changing the lengths of each path. Generally, a moving mirror is used to change the optical path lengths.
FIG. 1 shows one example of an interference spectrometer, such as described in Japan Patent Laid-Open 63/135,827, and comprising a beam splitter 1, a fixed mirror 2, a moving mirror 3, a compensator 4 and an air bearing 5. An incident light 100 is inputted to beam splitter 1. A part of the incident light 100 is reflected by beam splitter 1 and enters fixed mirror 2. The remainder of incident light 100 is transmitted through beam splitter 1 and compensator 4 and enters moving mirror 3. The light beams reflected from fixed mirror 2 and moving mirror 3 enter beam splitter 1 again and are outputted as interference light 101. Moving mirror 3 is provided on air bearing 5 and its position is controlled through control of air bearing 5.
FIG. 2 shows another example of an interference spectrometer, such as described in Japan UM 63/1,221, and comprising a beam splitter 1a, a fixed mirror 2a, a moving mirror 3a, diaphragms 6,7, and driving means 8.
An incident light 100a is inputted to beam splitter 1a and a part thereof is reflected by beam splitter 1a and enters fixed mirror 2a. The remainder of incident light 100a is transmitted through beam splitter 1a and enters moving mirror 3a. The light beams reflected from fixed mirror 2a and moving mirror 3a enter beam splitter 1a again and are outputted as interference light 101a. Moving mirror 3a is supported by diaphragms 6,7 and its position is controlled by driving means 8.
The example of FIG. 1, however, has a problem in that although air bearing 5 is used to smooth the motion of moving mirror 3, there is no restraint in the axial direction; hence, the mirror is subject to vibration in the axial direction.
The example of FIG. 2 also has problems in that although a certain degree of restraint in the axial direction is provided by diaphragms 6,7, a large sized diaphragm is required to move the moving mirror to any appreciable degree, and in that for all practical purposes the mirror must be driven by a large force, if restraint is strong, thereby necessitating use of a large amount of power.
There is also known a method of detecting the speed of the moving mirror by use of an interference signal from a He-Ne laser. However, in such a method, the band of the interference signal depends on the speed of the moving mirror, and control is affected thereby. Full control is difficult at lower speeds. Also, detectable resolution of the speed of the moving mirror is restricted to about one-half of the output wavelengths of the He-Ne laser.